Virtual MIDI Piano Keyboard is a MIDI event generator and receiver. It doesn't produce any sound by itself, but can be used to drive a MIDI synthesizer (either hardware or software, internal or external). You can use the computer's keyboard or mouse to play MIDI notes. You can use the Virtual MIDI Piano Keyboard to display the played MIDI notes from another instrument or MIDI file player.

Skype uses P2P (peer-to-peer) technology to
provide voice- and video-based communication with other Internet users. The technology is extremely
advanced, but easy to use. It features excellent
sound quality, end-to-end encryption, and
automatic negotiation of firewalls or routers.
Among major features are SkypeOut and SkypeIn,
adding the possibility to make low-cost calls to
land line phones and having a fixed number to be
able to receive calls from land line phones.

PyScape generates dynamic soundscapes using the OpenAL library which can be manipulated interactively via a GUI. Several CC-licensed sounds are included, such as the Buddha Machine loops and various nature sounds.

listener is a typical security-related program like the motion package (which detects motion on a Webcam): it listens for sound. If it detects any, it starts recording until the sound stops (or a bit later, which is configurable). It stores the audio in .WAV files.

The buzztard project aims to provide a free
replacement for the Windows-only and closed source
Buzz music production environment. It is based on
a very modular approch that allows many people to
get involved.

FB-Mix is designed to sit in the Fluxbox system tray and popup an alsamixer window when clicked. It should also work with other window managers. As of version 0.2, volume can also be adjusted using the mouse scrollwheel when hovering over the icon.

Mup produces very high quality PostScript printed music or a MIDI file from a text input file. It can handle almost any kind of music, instrumental or vocal, including tablature, shaped notes, guitar grids, alternate tunings, user-defined symbols, and much more. Mup has been under active development since 1992.

Python Audio Tools is a collection of audio handling programs that work from the command line. These include programs for CD extraction, track conversion from one audio format to another, track renaming and retagging, track identification, CD burning from tracks, and more. It supports internationalized track filenames and metadata using Unicode. It works with high-definition, multi-channel audio as well as CD-quality. Track conversion uses multiple CPUs or CPU cores if available to greatly speed the transcoding process. Track metadata can be retrieved from MusicBrainz, FreeDB, or compatible servers. Audio formats supported are WAV, FLAC, WavPack, MP3, Ogg Vorbis, M4A, Apple Lossless, and more.